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  1. #1

    Join Date
    May 2019
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    0

    How many amps are you drawing running your CNC___ on single phase?

    Hello, first time posting here.
    For all of you out there running VMC's and CNC turning centers with single phase residential power, Especially those that have the Phase perfect solid state phase converters.
    Have any of you measured the current on the 240V single phase input lines while the machine was operating?
    I ask this question because I plan to install a 40hp phase perfect (PT3110) to run a CNC turning center.
    The phase perfect literature recommends that the input be fed from a 250A two pole circuit breaker. This is all fine and good, but I am curious as to what the normal
    steady state amperage draw would be on my meter while running the cnc as normal. I understand there are many variables to this situation.
    (depth of cut, feeds and speeds programmed, multiple axis moving simultaneously, etc.)
    Please provide your findings, if any, by stating your CNC's placarded KVA rating, and the measured amperage of your input.

    My example would be; 45KVA machine, draws around ____A (measured with an amp clamp between the breaker and Phase perfect) on a typical run turning some 2" 4140 steel parts.

    thanks in advance for any help on this.

  2. #2

    Re: How many amps are you drawing running your CNC___ on single phase?

    I can't find a placard on my CNC lathe.

    240V, 3 phase, 7.5 KW (10 HP) spindle motor, 0.75 KW hydraulic pump

    Test Conditions:
    Run from a homebrew 15 HP rotary phase converter
    85% spindle load
    Hydraulic pump on
    Four 1.8 KW Axis servos on, but not moving

    Results, single phase feed measured at the input to the RPC disconnect:
    239V, panel gauge
    14.1 Amps, panel gauge, 13.9 Amps, Fluke true RMS clamp meter
    0.68 Power Factor, panel gauge.

    So about 3.4 KW apparent power, but including the power factor; about 5 KW or about 20 amps load on the line.

    I hope this helps.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
    Member
    Join Date
    Sep 2005
    Posts
    1360

    Re: How many amps are you drawing running your CNC___ on single phase?

    The 250 amp breaker is to cover your starting current. I doubt if your residential service is going to be able to start and run a 40 Hp motor. Biggest ones they put in around here is 200 amp service. Even if they did the service lines in the area would never be able to handle it.

    A 40 Hp motor could draw as much as 120 amps on three phase, since your on single phase input it would be more. What Jim has measured above and he will correct me, is under no load.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router

  4. #4
    Registered
    Join Date
    Nov 2012
    Posts
    126

    Re: How many amps are you drawing running your CNC___ on single phase?

    Ours is shown in this along with the plates it’s still not running though I’m wondering about the ground it is not staked to the ground.
    https://youtu.be/oy-zvg9sEIc

  5. #5

    Re: How many amps are you drawing running your CNC___ on single phase?

    Quote Originally Posted by wmgeorge View Post
    What Jim has measured above and he will correct me, is under no load.
    That's at 85% spindle load. The FLA on the spindle motor is 30 amps, the 3 phase legs out of the phase converter were running at about 23 amps each. I know, those are impossible numbers, but that is measured values. I have a magic RPC, it's an over unity device.
    Jim Dawson
    Sandy, Oregon, USA

  6. #6
    Member
    Join Date
    Sep 2005
    Posts
    1360

    Re: How many amps are you drawing running your CNC___ on single phase?

    Quote Originally Posted by Jim Dawson View Post
    That's at 85% spindle load. The FLA on the spindle motor is 30 amps, the 3 phase legs out of the phase converter were running at about 23 amps each. I know, those are impossible numbers, but that is measured values. I have a magic RPC, it's an over unity device.
    Believe it or not.... when I worked years and years ago (as a electrician) in a large gypsum plant where they crushed the rock from the quarry and all and it ended up as plaster board, and a few other products. The large roll mill had a 400 HP synchronous motor, that had DC exciting the field and I forget the details. But they used that large motor for correcting the power factor in the entire plant, by over exciting the field. So they effectively did away the the inductive load of all those AC 3 phase motors. That was nearly 60 years ago so the details might be a little fuzzy.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router

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